That was it. I set the UpdateScrolling(value) before filling the tooltip.
Reversed that order, data first, UpdateScrolling(value) later.

Worked :)

And I want a value.
Have a tooltip with my (online) guild members and am in a guild with 900+ members.
Usually 70 to 100+ members online.
And I don't want the tooltip to take up a big part of the screen.